1. Field of the Invention
The present invention relates generally to the field of helical pilings or screw piles. More specifically, the present invention discloses a piering device having a threaded shaft and helical bearing plate.
2. Statement of the Problem
Piering systems have long been used to lift and stabilize foundations of structures, and also in new construction. Some systems employ piles that are driven into the ground adjacent to the foundation, while other piering systems employ helical piles that are screwed into the ground. These piles are also used to anchor structures (e.g., large antennas, or pylons for high voltage lines) that are subject to large wind loads.
Conventional helical piles have an elongated shaft with a helical bearing plate permanently attached to the shaft adjacent to its lower end. The shaft can either be solid or tubular. For example, A. B. Chance Company of Centralia, Mo., markets helical piles having a solid shaft with a substantially square cross-section. The lower end of the shaft is beveled to form a point. The helical bearing plate is welded to the lower end of the shaft adjacent to the bevel. The length of the shaft is fixed, as are the diameter and location of the helical plate. In addition, some installations require several helical plates of different diameters spaced along the shaft. All of this can result in an substantial inventory problem to ensure that the appropriate helical piles are in stock for each job, particularly due to the size and expense of these helical piles.
It is also difficult to accurately predict the length of the piles that will be required for a specific job. Helical pilings are typically screwed into the ground to a point at which a predetermined torque limit is reached. It is difficult to predict what the depth of insertion will be when this torque limit is reached, due primarily to the unpredictable nature of local soil conditions. Therefore, it is often necessary to add an extension to the shaft of the helical pile. For example, A. B. Chance Company markets an extension shaft having a square socket that fits over the upper end of the helical pile shaft. A bolt can be passed through aligned holes in the socket of the extension shaft and the upper end of the helical pile shaft to secure the extension shaft to the helical pile. However, these holes significantly weaken the assembly.
A related problem arises if the shaft of the helical pile is too long. In this case, the upper end of the shaft must be cut off and a new hole must be drilled through the shaft to secure the shaft to the support bracket needed to engage the foundation. This can be difficult and time-consuming in the field.
Thus, a need exists for a helical piling system that is modular in design so,that helical plates of various sizes and diameters can be used interchangeably, and various helical plates can be interchangeably combined with a shaft of a desired length. In addition, there is a need to be able to quickly and easily connect shafts to one another in the field to create a shaft assembly of desired length.
Other examples of helical pilings that have been used in the past include the following:
Gray discloses a threaded pile with a threaded helical plate. After the pile has been driven into the ground, the plate 10 is advanced into the ground by rotating a handle 15 attached to a removable sleeve 13.
Dziedzic discloses a modular screw anchor having an earth-penetrating lead 16 that is separate from the helical plate 30. In the embodiment shown in FIGS. 2-6 of Dziedzic, the earth-penetrating lead and plate assembly are connected to a rectangular shaft. In the embodiment shown in FIGS. 7-10 of Dziedzic, the shaft is round with threads at its lower end to engage the earth penetrating lead 60.
Seider et al., Holdeman et al. and Gregory et al. disclose other examples of an apparatus for stabilizing the foundation of a building using a conventional helical piling that has been screwed into the ground.
U.S. Pat. Nos. 5,139,368 and 5,171,107 to Hamilton et al. disclose a system for underpinning a foundation that uses a helical pile with a connecting bracket secured to the foundation.
Schirm discloses a tie rod having a helical plate 3 and a moving foot 15 that can slide along the rod 2 limited by the position of a nut 31 threaded on the rod 2.
Grimaud is believed to relate to a pile foundation.
Reinert discloses a mobile foundation installation system having a push-it carriage that can push a metal foundation into the ground by hydraulic cylinders pushing against a header frame held and secured in adjustable positions on a mobile tower.
McFeetors et al. disclose a ground anchor system for supporting a structure. A fixed-length helical pile is driven into the ground. The upper end of the piling device includes a screw that allows adjustment of the height of the support head beneath the foundation.
Petersen discloses a screw anchor that receives a square shaft. The anchor is held in place by a pin extending through the anchor and the shaft.
Williams, Norman et al. and Hamilton et al. (U.S. Pat. No. 5,408,788) show examples of screw anchors that can be threaded onto the lower end of a shaft.
Jones discloses a support bracket for attachment to the top of a conventional helical piling.
None of the prior art references uncovered in the search show a helical piling with a threaded shaft and helical plate. This allows the appropriate helical plate(s) to be threaded on the shaft to meet the specific needs of each job. After the helical plate has been threaded to the desired location on the shaft, the helical plate is held in place by inserting a removable key into the longitudinal slot extending the length of the shaft. The shaft can also be cut to the desired length without waste.
The shaft and helical plate of a helical piling are subject to enormous torsional loads during installation, and very large axial loads (either in compression or tension) after the helical piling has been placed in use. None of the prior art references uncovered in the search teach or suggest a threaded arrangement with a removable key to transmit these loads.
The present invention is a piering device having a threaded shaft and a helical bearing plate with a threaded passageway that engages the threaded shaft. This allows the helical plate to be advanced to any desired location along the shaft. The helical plate can also be readily replaced with one or more helical plates of different sizes and diameters. The threaded shaft has a key way or slot extending along its length. The threaded passageway of the helical plate can also be equipped with a key way or slot. A key is removably inserted into the shaft key way and helical plate keyway after these key ways have been rotated into alignment to secure the helical plate at the desired location along the shaft.
A primary object of the present invention is to provide a helical piling having modular components that can be readily combined and configured to meet the requirements of a wide variety of jobs.
Another object of the present invention is to provide a helical piling that greatly minimizes inventory requirements.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.